The present invention relates to vent valves for fuel tanks, particularly fuel tanks for motor vehicles where it is required to control the venting of the fuel vapor to prevent escape to the atmosphere. Current production passenger cars and light trucks employ a: vapor storage device such as a canister filled with granular carbon for storing vapor during periods of engine shutdown for subsequent purge to the engine air inlet upon engine startup. Such systems employ a float operated vent valve in the tank to control the flow to the canister of fuel vapor in the vapor dome above the liquid level and particularly during refueling.
It is necessary to prevent liquid fuel from entering the vapor vent lines to the canister to prevent liquid blockage of the vapor vent lines. During refueling if the filler tube for refueling is completely filled to the top of the filler neck, which typically extends to a level above the top of the fuel tank, there is a danger that liquid fuel will flow through the vapor vent valve and enter and block the vapor vent lines.
In order to prevent liquid fuel from entering the vapor vent lines and potentially blocking the vent lines, it has been found satisfactory to provide a float operated vent valve which closes the vapor vent upon the fuel level reaching a predetermined level in the tank which can be chosen to be slightly below the top wall of the tank.
Known float operated vapor vent valves for fuel tanks have employed a disk or wafer type valve element caged on the top of the float, for limited lost motion with respect to the float, for sealing against a valve seat provided on the vapor vent line port at the; top of the fuel tank. However, in view of the minimal force applied by the float to the valve element by the forces of buoyancy acting on the float, it has been quite difficult to provide a complete seal and some leakage has been experienced.
The known valve constructions have employed an inclined or offset configuration to the cage to provide a peel-away action for the valve disk as the float is lowered by the falling level of the liquid as fuel is drawn from the tank during engine operation to ensure reopening of the vent line port after closure during refueling. Heretofore, the valve disk member has been formed of plastic material in order to prevent xe2x80x9ccorkingxe2x80x9d of the valve member on the port.
In such valves, where there is any angular misalignment between the top of the float and the vent port valve seat, it has been difficult to enable the float to completely close the valve member against the port valve seat. Thus, it has been desired to provide a way or means of ensuring a positive closure and seal of a float operated fuel vapor vent valve upon filling the tank during refueling and to ensure reopening of the vent port upon the fuel level falling from subsequent withdrawal of the fuel from the tank during engine operation.
The present invention provides a solution to the above-described problem with a float operated vent valve having a resilient elastomeric valve member with a thin flexible central region and an annular bead formed on the periphery with a rigid plate or disk contacting the annular bead during upward movement of the float to cause the central portion of the elastomeric member to seal on the vapor vent lock port valve seat in the top of the fuel tank. The valve member is caged upon the float for limited lost motion with respect to the float and the cage is configured with an inclined or offset upper portion to effect a peel-away action against the annular bead as the float moves downward during subsequent withdrawal of fuel from the tank. The rigid backing plate for the valve member is free to pivot about a fulcrum surface provided on the top of the float to effect self-alignment of the valve member on the vent port valve seat.